Percutaneous transluminal coronary angioplasty (PTCA) is used to increase the lumen diameter of a coronary artery partially or totally obstructed by a build-up of cholesterol fats or atherosclerotic plaque. Typically a first guidewire of about 0.038 inches in diameter is steered through the vascular system to the site of therapy. A guiding catheter, for example, can then be advanced over the first guidewire to a point just proximal of the stenosis. The first guidewire is then removed. A balloon catheter on a smaller 0.014 inch diameter second guidewire is advanced within the guiding catheter to a point just proximal of the stenosis. The second guidewire is advanced into the stenosis, followed by the balloon on the distal end of the catheter. The balloon is inflated causing the site of the stenosis to widen. The dilatation of the occlusion, however, can form flaps, fissures and dissections which threaten reclosure of the dilated vessel or even perforations in the vessel wall. Implantation of a metal stent can provide support for such flaps and dissections and thereby prevent reclosure of the vessel or provide a patch repair for a perforated vessel wall until corrective surgery can be performed. It has also been shown that the use of intravascular stents can measurably decrease the incidence of restenosis after angioplasty thereby reducing the likelihood that a secondary angioplasty procedure or a surgical bypass operation will be necessary.
An implanted prosthesis such as a stent can preclude additional procedures and maintain vascular patency by mechanically supporting dilated vessels to prevent vessel reclosure. Stents can also be used to repair aneurysms, to support artificial vessels as liners of vessels or to repair dissections. Stents are suited to the treatment of any body lumen, including the vas deferens, ducts of the gallbladder, prostate gland, trachea, bronchus and liver. The body lumens range in diameter from small coronary vessels of 3 mm or less to 28 mm in the aortic vessel. The invention applies to acute and chronic closure or reclosure of body lumens.
A typical stent is a cylindrically shaped wire formed device intended to act as a permanent prosthesis. A typical stent ranges from 5 mm to 50 mm in length. A stent is deployed in a body lumen from a radially compressed configuration into a radially expanded configuration which allows it to contact and support a body lumen. Many stents are designed to be expanded by the use of an expansion device within a body lumen. As a result, the stents are typically manufactured from materials that are plastically deformable. A plastically deformable stent can be implanted during a single angioplasty procedure by using a balloon catheter bearing a stent which has been crimped onto the balloon. The stent expands radially as the balloon is inflated, forcing the stent into contact with the interior of the body lumen thereby forming a supporting relationship with the vessel walls. After deployment, the biocompatible metal stent props open blocked coronary arteries, keeping them from reclosing after balloon angioplasty.
The problems facing those attempting to crimp stents onto expandable delivery devices, such as balloon catheters, are numerous. In some instances, the stents are manually crimped onto the delivery device using finger pressure or pliers. Such crimping can however, result in damage to the stent during handling prior to use as well as during the act of crimping because of the lack of control over the forces used during crimping. In either case, the damaged stents cannot be used. Furthermore, if the damage to the stent is not noticed, the stent may fail to perform as intended after deployment. In addition to damage to the stent itself before or during crimping, the crimping process can damage the delivery device if the forces applied during crimping are excessive.
Even if the stent and/or the delivery device are not damaged, other potential problems remain. For example, the stent may be non-uniformly crimped onto the delivery device which can cause problems during advancement of the stent to the desired location within a body lumen and/or during deployment of the stent.
Other problems include maintaining sterility of the stent. To assist with maintaining sterility, it is often preferred that the crimping devices be disposable such that they can be discarded after a single use. By disposing of the crimping device, the chance of cross-contamination originating with the crimping device itself can be eliminated.
Examples of crimping devices for stents are known, such as U.S. Pat. No. 5,626,604 to Cottone, Jr. which discloses a stent crimping device including a collet for radially crimping a stent onto a catheter. The collet includes radially compressible members that are compressed by use of sliding collet or a rotating collet.
U.S. Pat. No. 5,672,169 to Verbeek discloses a manual stent crimping device in which the stent is mounted between four comer blocks, with the upper and lower pairs of comer blocks being separated by compressible members. Compression of the upper and lower pairs of comer blocks forces the stent diameter to decrease, thereby crimping the stent onto a delivery device extending through the stent.